The present invention relates to mixes based on fluoroelastomers containing Br or J, additioned with particular organic peroxides, which exhibit, during curing, a low emission of toxic vapors of methyl bromide or iodide.
The cure with organic peroxides of the fluoroelastomers containing, as cure sites, bromine or iodine atoms along the polymeric chain and/or at the end of said chain is broadly known.
In such fluoroelastomers, bromine or iodine are introduced into the elastomer macromolecule by using, during the polymerization step, brominated or iodidated comonomers such as, in particular, fluorobrominated olefins, brominated or iodidated fluorovinyl ethers or by using, in the polymerization itself, brominated or iodidated compounds as chain transfers.
In the peroxide cure of said elastomers there are utilized, in general, organic peroxides of the aliphatic type, either saturated or unsaturated, such as e.g.: 2,5-dimethyl-2,5-di(ter.butylperoxy)hexine-3 2,5-dimethyl-2,5-di(ter.butylperoxy)hexane, which give rise, in the curing process, to the formation of methyl radicals. These radicals, by combination with bromine or iodine contained in the fluoroelastomer, form methyl bromide or iodide, which are highly toxic volatile products and, as regards iodide, also a cancerogenous product.
Therefore, while the peroxide curing of fluoroelastomers containing Br or I permits to obtain cured articles having improved stability to steam and to other aggressive agents as compared with the articles obtained through a ionic curing, it is apparent, on the other hand, that said peroxide curing involves a serious hazard for the health of the operators entrusted with the processing of said elastomers.
Furthermore, it is not possible to avoid the drawback caused by said harmful emissions merely by using peroxides which do not release at all or release only little amounts of methyl radicals during their decomposition, because said peroxides could not cure at all or only weakly cure said fluoroelastomers. That is apparent, for example, when using organic perketalic peroxide of formula: ##STR2## which, by decomposition, prevailingly provides ethyl radicals and only little amounts of methyl radicals, but which is not capable of curing the fluoroelastomers containing bromine or iodine.